The objective of this proposal is to develop methods which will noninvasively measure anatomic and hemodynamic variables concurrently in the left main and left anterior descending coronary arteries. Clearly, a more thorough evaluation of atherosclerotic involvement can be made if noninvasive flowmetry is combined with vessel imaging. By considering blood velocity variables and estimated flow information, the hemodynamic significance of imaged lesions as well as distral, undetected lesions can be estimated. Hopefully, improved clinical and/or surgical management of the patient will result along with a more selective use of cardiac catheterization. We propose to utilize the Advanced Technology Laboratories (ATL) Mark V Two Dimension Real-time Echocardiographic Duplex Scanner (EDS) as the base instrument for our studies. By significantly modifying this commercially available EDS and developing modular components which will allow the sample volume to track the coronary vessels, back-scattered Doppler audio spectra generated from the moving blood particles will be recorded concurrently with the two dimensional "tracked" image of the coronary vessel. The high resolution image of the interrogated vessel will be used to help detect significant lesions. Equally important, the Doppler audio spectra will be used 1) to help identify focal flow disturbances created by subcritical, nonimaged lesions, 2) to calculate blood velocity patterns which may reflect changes in the input impedance to the distal myocardial vascular bed created by unresolvable distal lesions or coronary vasospasm, and 3) to estimate blood flow rates and hence regional perfusion which may be compromised by hemodynamically significant lesions. The instrumentation will be evaluated in vitro using physical models and excised human arteries. In vivo comparisons will be made between simultaneously obtained invasive and noninvasive measurements from human patients undergoing diagnostic cardiac catheterization. A blind study using the newly developed instrumentation will be conducted in a series of patients undergoing diagnostic cardiac catheterization. The noninvasive studies will be conducted independently and a noninvasive diagnosis of the presence and significance of coronary disease will be compared blindly to the subsequent angiographic diagnosis. This preliminary clinical study will evaluate the new system in identifying and quantifying left coronary artery disease.